泥石流坝后溯源淤积过程研究——以大盈江浑水沟为例

The debris flow check dam is an important engineering means to prevent the risk of debris flow disasters, because it has the functions of blocking, energy dissipation, gully fixing and slope stabilization. The sedimentation process and morphology of debris flows behind the check dam directly affect the function of the dam. The relevant research domestic and abroad shows that: the original ditch bed slope, dam height, dam type, debris flow size, bulk density and particle composition are the main factors controlling the deposition process and morphology behind the check dam. However, most of these understandings are derived from model experiments, lacking the test of real debris flow blocking projects. Therefore, the objective laws are difficult to reveal. Combined with FLO-2D technology, this study intends to use the long-term field data of 50 years of Hunshui Gully debris flow in Yunnan Province (the observation of debris flow before dam construction, the dynamic process measurement of deposition and rainfall observation after dam, etc.). It analyzes the precipitation-debris flow process before and after the dam construction, the sedimentation process and morphology of debris flows with different dam height, different scale and volume density behind the check dam, the influence of debris flow siltation and the flood erosion interaction on the deposition behind the check dam, and the key parameters of the deposition process (deposition slope, thickness and velocity, etc.). The paper discusses the actual function of blocking, energy dissipation, gully fixing and slope stabilization in the Hunshui cascade dam group and its time series evolution. It reveals the headward deposition process and mechanism of the debris flow check dam, establishes the calculation method of the limit silting gradient behind the debris flow dam and provides the theoretical basis for the calculation of the key parameters of the dam.

泥石流拦砂坝具有拦蓄、消能、固沟和稳坡等功能，是防范泥石流灾害风险的重要工程手段，坝后泥石流淤积过程和形态直接影响拦砂坝的功能。国内外相关研究表明：原沟床坡度、坝高、坝型、泥石流规模、容重和颗粒组成等是控制坝后淤积过程和形态的主要因素，但这些认识多源于模型实验，缺乏真实泥石流拦挡工程的检验，客观规律难以揭示。本研究拟利用云南省浑水沟泥石流50多年的长时序野外数据（建坝前泥石流观测、建坝后淤积动态过程测量、降雨观测等），结合FLO-2D技术，分析建坝前后降雨-泥石流流量过程、不同坝高不同规模及容重泥石流坝后淤积过程和形态、泥石流淤积-洪水冲刷交互作用对坝后溯源淤积的影响、以及溯源淤积过程关键参数（淤积坡度、厚度和速率等），探明浑水沟梯级坝群主要功能的时序演变特征，揭示泥石流坝后溯源淤积过程及机理，提出泥石流坝后淤积极限平衡坡度计算方法，为泥石流拦砂坝关键参数计算提供理理论依据。

泥石流拦砂坝是泥石流防治较为有效的工程措施，泥石流坝后淤积过程受多种因素的影响，已有的认识多源于模型实验，缺乏真实泥石流拦挡工程的检验，客观规律难以揭示，亟待开展基于过程的长时序的泥石流溯源淤积过程的研究。.本研究选取我国泥石流防治工程的典范工程——浑水沟梯级拦砂坝，项目以长时序泥石流野外历史观测资料为基础，结合现场综合观测及室内实验，明晰了浑水沟坝后泥石流淤积主控因素演变特征；厘清了浑水沟坝后泥石流溯源淤积过程及机制；揭示了长时序泥石流堆积物土壤理化特性及土壤生产力演变过程；揭示了长时序支沟泥石流活动影响主河河床演变的过程及规律。项目主要研究结果如下：.（1）梯级拦砂坝群在浑水沟泥石流活动控制上发挥了关键作用，泥石流由治理前每年50余次降低至现在每年4-6次支沟泥石流；侵蚀基准面抬高了152 m，坝群整体拦蓄了1008.42万m³的泥石流固体物质。坝后淤积呈现出沿主流淤积和淤积速率先升后降的趋势，后期出现溯源淤积现象。（2）梯级拦砂坝群建设和溯源淤积的出现极大增强了山体稳定性，在梯级拦砂坝群高度与滑坡剪出口高度基本一致时，开始发挥稳定山体功能。浑水沟梯级拦砂坝群稳定固体物源的量约3040.88万m³，削弱了流域产沙量，梯级拦砂坝群整体减少超过4000万m³的泥沙输出。（3）泥石流滩地土壤生产力的恢复呈缓慢的过程，其中土壤生产力指数和土壤有机质呈指数型增长；23年的恢复年限很可能是坝后泥石流堆积物土壤生产力恢复的阈值时间。（4）浑水沟泥石流活动强烈改变主河水沙关系，导致河床淤积抬升、形成游荡型河床；极端泥石流事件造成主河堵溃，造成下游极端洪水灾害；泥石流防治有效减少入汇主河的泥沙，主河重新恢复原有水沙关系，河床演变为侵蚀下切、河床由游荡型转变为稳定河床。.研究科学监测和评估了重大泥石流灾害防治效果，明晰了长时序泥石流坝后淤积过程及规律，研究成果为泥石流防治工程的后期维护提供技术保障，为山区梯级拦砂坝功能演变提供案例参考。